Anaconda's GTK UI and the backend are running in the same thread. GTK is unfortunately not designed to be run in the same thread as the app. Although this arrangement sort of works for the moment problems can be noticed: for instance on a virtual machine (slow) there is a visible lag between the time "scanning storage devices" dialog pops up and the time this dialog gets window decorations by metacity. What we do at the moment when we want to update the UI and the processing happens outside of the gtk.main function is calling gtk.main_iteration(False) (or window.show_now())to manually enforce one gtk main loop. Coming to #pygtk at gnome's IRC I was repeatedly told by the gurus that this is a hack bound to randomly fail to accomplish what we expect.

Also separating the threads will allow us to do certain tasks in the background, not blocking the user from continuing with other parts of installation. For instance Anaconda can already be initializing the filesystem while the user is picking packages to be installed.